Engineering plastics are widely used in various fields including office automation (OA) equipment, telecommunications equipment, electrical and electronic equipment, home appliances, automobiles and construction due to their superior mechanical strength, heat resistance, electrical characteristics, dimensional stability and so forth. However, they also have the problems of a high molding and forming temperature and inferior melt fluidity in the case of, for example, polycarbonate resins.
On the other hand, in the case of their molded products being used in the housings and parts of OA equipment such as photocopiers, facsimiles and personal computers, telecommunications equipment or electrical and electronic equipment, there has recently been a need for resin modifiers and compositions that enhance the melt fluidity, namely injection moldability, of polycarbonate resins due to the increasingly complex shapes of these molded products, the molding of lines, indentations and other surface irregularities in these molded products, and the use of increasingly thin-walled molded products in consideration of lighter weight and resource conservation.
In improving the melt fluidity of polycarbonate resin, (1) a typical method involves reducing the molecular weight of the polycarbonate itself serving as the matrix resin. In addition, fluidity has also been reported to be improved by forming a polymer alloy from a styrene resin and a polycarbonate resin such as a polymer alloy composition with acrylonitrile-butadiene-styrene resin (ABS plastic), a polymer alloy composition with a styrene resin such as rubber-denatured polystyrene resin (high impact polystyrene, HIPS), or a polymer alloy composition with acrylonitrile-styrene resin (AS resin) (Japanese Examined Patent Application, Second Publication Nos. 38-15225, 43-6295 and 43-13384).
In addition, methods that have been proposed for the purpose of further improving fluidity include (3) a method in which a polyester oligomer is added (Japanese Examined Patent Application, Second Publication No. 54-21455), (4) a method in which an oligomer of polycarbonate is added (Japanese Unexamined Patent Application, First Publication No. 3-24501), (5) a method in which a low molecular weight styrene copolymer is added (Japanese Examined Patent Application, Second Publication No. 52-784, and Japanese Unexamined Patent Application, First Publication No. 11-181198), (6) a method in which a polymer having a polyorganosiloxane segment is added (Japanese Unexamined Patent Application, First Publication No. 11-35831), and (7) a method in which a polymer obtained by polymerization of styrene is added in the presence of polyalkyl(meth)acrylate (Japanese Unexamined Patent Application, First Publication No. 2000-239477).
However, although the method of (1) in which the molecular weight of the polycarbonates self is reduced greatly improves fluidity, due to reducing the molecular weight beyond that which is necessary, the superior impact resistance and heat resistance of the polycarbonate is lost. In addition, since chemical resistance also decreases, there are limitations on improving melt fluidity by lowering molecular weight while maintaining the superior characteristics of polycarbonate.
In addition, the formation of a polymer alloy from styrene resin and ABS resin or HIPS resin of (2) is used in numerous molded material fields by taking advantage of its superior characteristics of heat resistance, impact resistance and fluidity. However, due to the increasing complexity of the shapes of injection molded products in recent years, the molding of lines, indentations and other surface irregularities in these molded products, and the use of increasingly thin-walled molded products in consideration of lighter weight and resource conservation, resin modifiers and compositions that flirter enhance the fluidity, and namely injection moldability, of polycarbonate resins are required. In order to obtain effective fluidity with such polymer alloy compositions, it is necessary to increase the blended amount of ABS resin and so forth, thereby placing limitations on improvement of fluidity while maintaining the superior characteristics of polycarbonate in the form of heat resistance, impact resistance and flame resistance.
In addition, although the method of (3) involving the addition of a polyester oligomer and the method of (4) involving the addition of a polycarbonate oligomer are effective for improving fluidity, they have the problem of causing a significant decrease in the superior heat resistance and impact resistance of polycarbonate.
In addition, the method of (5) in which a low molecular weight styrene copolymer is added makes it possible to improve melt fluidity to a certain extent while maintaining heat resistance. However, in addition to the effect on improvement of fluidity being inadequate, since this low molecular weight styrene copolymer also has insufficient compatibility, molded products are susceptible to the occurrence of surface layer separation while also resulting in accompanying problems of insufficient impact strength, weld appearance, which is important for practical use, and surface impact. In order to improve this compatibility, methods are employed in which are added a low molecular weight AS resin, aromatic vinyl resin having a polar group with an SP value of greater than 9.3 to less than 11.5, and copolymer consisting of a (meth)acrylate ester having a functional group such as an epoxy group and an aromatic vinyl compound (Japanese Unexamined Patent Application, First Publication Nos. 8-127686, 11-181197 and 2000-239477).
However, as will be described in the examples, these are merely copolymers consisting of low molecular weight styrene and a polar monomer, and although ice layer separation is improved by improving compatibility, effects for improving fluidity still remain inadequate, thus resulting in the problem of impact resistance decreasing is a large amount is added to improve fluidity.
In addition, in the method of (6) in which a polymer having a polyorganosiloxane segment is added, and in the method of (7) in which a polymer is added that has been obtained by polymerizing styrene in the presence of a polyalkyl(meth)acrylate, melt fluidity can be improved considerably while maintaining satisfactory heat resistance of the polycarbonate resin. However, due to inadequate compatibility, surface layer separation occurs easily in molded products while also leaving accompanying problems of inadequate impact strength, weld appearance, which is important for practical use, and surface impact.
On the basis of the above, all of the examples of the prior art are still inadequate with respect to improving melt fluidity without impairing the superior characteristics of engineering plastics as exemplified by polycarbonate.